Generally manufacturers supply three important pieces of information. These are RPM per volt (kV), maximum output power in watts and maximum current draw. All three should be used in selecting the optimum propeller. The RPM per volt (kV) is useful in determining the NO load motor RPM, the actual motor RPM achieved will vary with propeller loading. Just multiply the kV by the battery voltage under load to achieve the motor revs per minute (RPM). Unless the motor is to power a ducted fan model or drive an electric helicopter avoid high kV motors. A typical kV range for non-ducted fan, fixed wing models is 800 to 1200.
Unlike IC motors, the efficiency / power output graph of an electric motor is very narrow. To small a propeller = less thrust than the motor is capable off. Too large a propeller = less thrust and increased current draw / shorter flight times with the added danger of damaging the motor, ESC and battery. An indication of how hard the 'electrics' are working is how hot they get, assuming they are adequately ventilated. They should get warm but not hot. This means choosing the right propeller is critical for optimum performance and may require trying a selection of propellers before finding the one most suitable for that particular model.

If you increase the battery voltage i.e. cell count and the motor is operating at maximum recommended power then the propeller must be changed for one with less pitch and or reduced diameter. Remember power (watts) is the multiple of Voltage x Amps so increasing the voltage means that you must reduce the current (Amps) to stay within the maximum permitted power (Watts) to avoid damaging the motor. One reason why modellers increase battery voltage is to reduce current consumption to either increase flight times or overcome a battery's inability to deliver the current required to produce maximum power. Very occasionally motor information is available showing thrust per watt for a range of battery / propeller combinations to assist in choosing the right one.  Generally ARTF models are supplied with recommended combinations which assists selection of correct components.  The recommendations are usually accurate for the model so unless you are competent in assessing alternative component performance then it is best to stay with the recommended solution.

A final point for consideration when selecting a motor is the that maximum power rating (watts) is usually only attainable on the maximum battery voltage i.e. max cell count due to the current considerations mentioned above. This means that when selecting your motor you must multiply the max. current rating of the motor by the voltage of the battery you intend using to determine the power it will produce with the correct propeller. As an example, if the max. power of a motor is 500w, max current is 40A and max voltage is 14v (4 cell LiPo) it can only produce 500w at 14.8v. On a 3 cell LiPo pack (11.1v) it will only produce 444w due to the current limit of 40A (11.1 x 40). On a 2 cell pack (7.4v) it will on be 296w (7.4 x 40).
Brushless Electric Motors